Netcat is described as the Swiss Army Knife for TCP/IP. I use it in two different ways:
1) Build a small server that dumps the contents it receives to a file. (Helpful for reverse engineering and debugging purposes)
$ nc -l -p 10000 > out.txt
This will set netcat to listen on port 10000 and redirect the output to the file out.txt
For Instance, I configured a client program that sends messages to a server and connected to my localhost:10000 instead:
$hd out.txt
00000000 00 4d 30 31 30 30 70 2000 00 00 c0 00 00 31 36 |.M0100p ……16|
00000010 34 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |4111111111111111|
00000020 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 31 |0000000000000001|
00000030 30 30 31 32 33 34 35 36 31 32 33 34 35 36 30 31 |0012345612345601|
00000040 31 32 33 34 35 36 30 31 30 31 30 31 30 31 20 |12345601010101 |
This shows me that there is a 2 byte header (00 4d) of 77 bytes in front of this ISO8583 0100 (30 31 30 30) message.
2) Use it as a client to send message dumps. (Helpful for a quick and dirty method to send data over TCP/IP)
$ cat out.txt | nc localhost 10000
This will send the contents of out.txt and ‘pipe’ it to netcat that will attempt to connect to localhost on port 10000 and send the contents of out.txt.
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